Union pay for party and sport (11,8)
I believe the answer is:
association football
'union pay for party and sport' is the definition.
I can't tell whether this defines the answer.
'union pay for' is the wordplay.
'union' becomes 'association' (association is a kind of union).
'pay for' becomes 'football' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'association'+'football'='ASSOCIATION FOOTBALL'
Can you help me to learn more?
(Another definition for association football that I've seen is " Soccer".)